This objectives of this core are to support the research activities of the Program with regard to gastrointestinal and hepatic complications of marrow transplantation, and to carry out clinical research relevant to our patients. The core participates in the design of protocols, provides a uniform approach to the diagnosis and scoring of gut and liver complications, assures that clinical specimens used for research purposes are obtained and processed correctly, and follows patients longitudinally throughout their course. The core performs immunohistochemistry and in situ hybridization on biopsy specimens for research purposes, and processes blood samples and biological fluids for biochemical analysis. Clinical research activities proposed include: 1) a pilot study of oral beclomethasone dipropionate for the treatment of acute graft-versus-host disease of the intestine, followed by a randomized trial if there is evidence of safety and efficacy, 2) randomized trials of ursodeoxycholic acid (a bile acid which is less harmful to cell membranes than native bile acids) for patients with chronic GVHD and for patients with acute hepatic GVHD unresponsive to therapy with prednisolone, 3) biochemical analysis of gallbladder sludge, and a randomized trial of ursodeoxycholic acid for dissolution of gallbladder sludge which forms after transplantation, and 4) determination of the prevalence of hepatitis-C virus (by polymerase chain reaction) and anti-HCV, clinical outcomes, and long-term consequences of HCV infection in transplant patients.